Side wall seal for floating tank roofs



Sept. 18, 1951 Filed Nov. 5. 1945 SIDE J. H. wlGGlNs 2,568,529

WALL SEAL FOR FLOATING TANK ROOFS 4 Sheets-Sheet l www INVENTOR; H. WIGG/Ns doHN ATTORNEY .1. 1-1. wlGGlNs SIDE wALL SEAL FOR FLOATING TANK RooFs spL 18, 1951 4 Sheets-Sheet 2 Filed Nov 5, 1945 FIG.6.

:5 NG EN.. WW. n Q .mHNw .N. A wm J Y B W Sept. 18, 1951 J. H. wlGGlNs SIDE WALL vSEAL FOR FLOATING TANK RooFs 4 Sheets-Sheet 3 Filed Nov. 5, 1945 FIG.7.

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Sept. 18, 1951 J. H. wlGGlNs 2,568,529

SIDE WALL SEAL FOR FLOATING TANK ROOFS Filed Nov. 5, 1945 4 sheets-sheet 4 F IG IO. HALF c//ecLE 11: New WAY K coNsrANr .SHOE MEMBERS FOLLOW S105 WALL TRAVEL. CENTER 0F 5HoE MEMBER Roo/F Hao/US AND CENTER TRAVEL CENTER -oFHoE MEMBERS HALF CIRCLE I OLD WAY /f VAE/E5 ACCOUNT CENTER 0F SHOE MEMBEEJ MovE 0N BooF EAD/us INVENTO/ JOHN H. W/GG/MS ATTORNEY Patented Sept. 18, 1951 SIDE WALL SEAL FOR FLOATING TANK ROOFS John H. Wiggins, Chicago, Ill.

Application November 5, 1945, serial No. 626,854

2 Claims. 1

`This invention relates to oating tank roof seals, and particularly, Wiggins type seals of the kind that vcomprise a vertically-disposed annular shoe arranged in sliding engagement with the side wall of the tank and composed of (a) a plurality of segmental, metal shoe members arranged in spaced relation, and (bl) fabric sealing elements attached to the ends of said segmental shoe members so as to bridge the gaps or spaces between adjacent shoe members.

It is well recognized that when a circular floating roof is supported by a body of liquid confined in a tank provided with a circular side wall, the roof will not always remain in concentric relationship with the tank side wall, but at times, will move relatively to said wall and assume an eccentric position. It is also well recognized that when a metal tank is filled with liquid, the side wall of the tank at times will go out of round or assume a substantially oval form, thereby causing two diametrically-opposed portions of said wall to move inwardly towards each other, and cause the intermediate, diametrically-opposed portions of said wall to move outwardly or spread further apart. Bearing in mind that there is a space between the peripheral edge of the iioating roof and the tank side Wall, the above mentioned deformation of the tank side wall causes those portions of said space bounded by the inwardly-v displaced portions 'of the tank side wall to diminish in area and causes those portions of said space bounded by the outwardly-displaced portions of the tank side wall to increase in area.

In eifect,the tank side wall portionawhich constitute the outer perimeters of the spaces of reduced area shorten or diminish in length, and the tank side wall portions which constitute the outer perimeters of the spaces of increased area elongate or increase in length.

In an annular side wall shoe of the particular kind mentioned, contact of the shoe members with the tank side wall is maintained by mounting said shoe members on the roof in such a manner that said members are capable of moving inwardly and outwardly relatively to the peripheral edge of the roof. Prior to my present invention such an annular side wall shoe was so designed or constructed that when the segmental shoe members moved outwardly, the spaces between the ends of said shoe members increased in width, and when said shoe members moved inwardly, the spaces between the ends of the shoe members decreased in width. This necessitated the use of fabric sealing elements between the ends of the shoe members, of a width sifcient 2 to accommodate or provide for the abnormally wide spaces between the ends of the shoe members located in the zones of the outwardly-displaced or elongated portions of the tank wall when the tank wall goes out of round. The general practice was to make the fabric sealing elements between the shoe members approximately twice as wide as would be necessary to accommodate or provide for the spaces existing between the shoe members if the tank side wall always remained in a truly circular condition. For example, if fabric sealing elements 4 inches wide would provide for the relative movement between the ends of the shoe members if the tank side wall never went out of round, it would be necessary to use fabric sealing elements having about 8 inches of circumferential width, in order to bridge the gaps between certain of the shoe members when the tank side wall went out of round. Such excessively wide fabric sealing elements were not eilicient for stopping evaporation, be#- cause the wrinkles or folds which inevitably formed in some or all of said sealing' elements, tended to produce relatively large air or gas passageways between the tank side wall and the annular shoe or side wall seal of which said fabric elements formed a part. They also were objectionable, in that they made it necessary to provide excessive fullness in the conventional flexible, primary sealing member that closes the vspace between the peripheral edge of the oating roof and the annular side wall shoe and Whose outer peripheral edge is attachd in a gas-tight manner to the metal segmental shoe members and to the flexible sealing elements that close the gaps between the ends of said shoe members. In instances where the roof sealing structure comprises a Wiggins type secondary seal formed by a piece of gas-tight fabric attached to the annular side wall shoe and projecting upwardly from same so as to press against the tank side wall at a 'point above the top edge of said annular shoe, excessive fullness, folds, or deep wrinkles in the fabric sealing elements attached to the segmental members of the side wall shoe, make it necessary to provide equal fullness in the fabric constitut` ing the secondary seal, thereby reducing very greatly the efficiency of the secondary seal, as well as increasing the cost of the structure, and complicating the operation of attaching the secondary seal to the annular side wall shoe.

`The main object of my present invention is to increase the efficiency, reduce the cost, and simplify the operation of constructing a floating 'roof sealing structure of the kind that comprises an annular side wall shoe composed of a plurality of segmental metal shoe members arranged in spaced relation and fabric sealing elements attached to the ends of said segmental members so as to close the gaps or spaces between the ends of said members, especially when a secondary seal ofI the Wiggins type is mounted on the annular side wall shoe. To this end I proportion and combine the coacting segmental shoe members and fabric sealing elements of the annular shoe in'such a way, and mount said shoe membrs on the floating roof in such a manner, that mvment of the tank side wall relatively to the roof, caused by 'said wall going out of round, re'- sults in the shoe members and also the fabric elements, moving circumferentially relatively to the roof, sufficiently to maintain the annular shoe in contact with the tank side wall Without substantially varying or changing the width of 'the spaces between the segmental shoe members bridged by the fabric sealing elements. The preferred way of combining the segmental metal shoe members and the fabric sealing elements, is to make said sealing elements of such width that said elements are stretched out straight, or practically so, when the annular shoe is located in the zone of the tank side wall that is of maximum internal circumference, and provide pulling devices and pushing devices that determine the maximum and minimum width of the spaces between the shoe members, and cause the shoe members to move as a unit, circumferentially of the roof, without straining the fabric sealing elements, or producing wrinkles in same that reduce the efficiency of the sealing structure, or interfere with the attachment of the primary and secondary seals to the annular side Wall shoe. The segmental shoe members are mounted on the floating roof so that in addition to being capable of moving inwardly and outwardly towards and away from the tank side wall, said shoe members are also .capable of moving circumferentially relatively to the roof. A side wall shoe of the kind above described is particularly adapted for use with a tank side wall composed of a pluralityof lapped rings of gradually decreasingvinternal circumference from the lower end to the upper end of the wall, the bottom ring being of the largest internal circumference with successive rings set one inside of the other and reduced in circumference by an amount equal to the thickness of the metal plates of which the rings are constructed. When used with such a lapped ring side wall, the coacting elements of the annular side wall are so proportioned, that when said shoe is in the zone of the lowermost ring, the fabric sealing elements of said shoe are substantially straight and free from wrinkles, and as the roof rises in the tank, the fabric sealing elements of the shoe slacken slightly at each succeeding zone or ring of reduced diameter. In a tank of 120 ft. diameter, the inside circumference of the top ring of the side wall is about 1l inches shorter than `the inside circumference of the bottom ring. Accordingly, if the shoe members of the annular side vvall seal are made of convenient length, said seal would comprise forty shoe members, and the fabric sealing elements attached to the ends of said shoe members would be made of such width that the annular seal or shoe would be capable of reducing in circumferential length approximately 11 inches. In other words, in designing or constructing a side wall shoe for a tank of lapproximately the size mentioned, each of the fabric sealing elements of the shoe would only have to have a fullness of approximately one fourth of an inch, as this is the amount each fabric element would contract during the upward movement of the roof from the side wall zone of maximum cir-V cumferential length to the side wall zone of minimum circumferential length.

From the foregoing, it will be seen that my improved annular side wall shoe operates on a new principle, in that the segmental shoe mem# bers are not intended to move relatively to each other to provide for or accommodate out of roundness of the tank side wall, and in the functioning of said shoe, when the tank side wall deforms or moves relatively to the roof, the width of the spaces between the shoe members remain constant, or practically so, thereby overcoming the necessity of providing excessive fullness in the fabric sealing elements to accommodate such movement of the tank side wall. In instances Where the annular shoe is used with a lapped ring side wall, there is a slight reduction in the width of the spaces between the'shoe members as the length of the internal circumference of the shoe decreases progressively during the upward movement of the roof, but this reduction or decrease in the width of said spaces is so slight that the resultant slackening or puckering of the fabric sealing elements is negligible. It will also be seen that said annular shoe is of novel construction, in that the spaced shoe members are operatively combined with a means that pushes and pulls the shoe members circumferentially when the shoe is adapting itself to the tank wall, said means acting to control or determine the maximum and minimum circumferential length of the side wall shoe.

In the accompanying drawings which illustrate the preferred form of my invention, Figure l is a fragmentary, side elevational View of my improved annular side wall shoe, showing two of the segmental metal members of said shoe, a portion of the flexible primary seal that closes the space between the shoe and the peripheral edge of the floating roof, and a portion of the secondary seal attached to the upper end of the side wall shoe, said view being taken from a point looking outwardly from the roof towards the side wall of the tank.

Figures 2, 3 and 4 are horizontal sectional views, taken on the lines 2-2, 3--3, and 4-4 of Figure l.

Figure 5 is a fragmentary vertical sectional view, through the tank side wall and a portion of the floating roof, showing one form of mechanism that may be used to mount the annular side wall shoe on the roof, the point at which said View is taken being indicated bythe section line 5-5 of Figure l.

Figure 5a is an enlarged fragment of Figure 5.

Figure 6 is a top plan view of the floating roof, showing diagrammatically the hangers usedto mount the annular shoe on the roof.

Figure 7 is a vertical sectional View, on an enlarged scale, of the type of tank side wall with which my improved shoe is particularly adapted for use, i. e., a riveted side wall composed of a plurality of lapped rings of gradually decreasing internal circumference.

Figure 8 is a fragmentary side elevational view, illustrating a means of different construction from that shown in Figure l, for determining the maximum and lminimum circumferential length of the side wall shoe and for causing the shoe members and fabricv sealing elements to 5 move as a unit, circumferentially, relatively to 'the roof, some of the parts of the structure being omitted for the sake of clarity.

Figure 9 is a horizontal sectional view, taken on the line 9-9 of Figure 8; and

Figures 10 and 11 are views intended to illustrate, diagrammatically, the difference between the old way and my new way of constructing an annular side wall shoe composed of a plurality of spaced segmental shoe members and fabric sealing elements that bridge the gaps between said shoe members, said view containing legends that explain the principle of operation of said old and new side wall shoes.

In the accompanying drawings, the reference character E designates a floating roof that is supported by liquid conned in a tank, C designates `a plurality of segmental metal shoe membersthat are arranged in spaced relation and which form sections of an annular side wall seal or shoe that bears against the tank side wall, F designates vertically-disposed fabric sealing elements attached in any suitable gas-tight manner to the ends of adjacent shoe members C, so as to bridge the gaps or spaces X between saidl members, I-I designates a conventional primary seal, herein illustrated as being formed by a piece of gas-tight fabric whose inner edge is attached tothe floating roof by a means designated as an entirety in Figure 5 by the reference character I9, and whose outer edge is attached to the shoe members C of the side wall shoe by clamping rods l8L acted upon by clamping plates 2 carried by bolts 3 that project inwardly from said shoe members, as shown in Figure 2, and G designates a conventional Wiggins type secondary seal that projects upwardly from the annular side wall shoe and bears against the tank side Wall at a point above said shoe, said secondary seal usually being formed from a piece of gas-tight fabric whose lower end is attached to the shoe members by 'clamping rods I acted upon by the previously mentioned `clamping plates 2, and whose upper end is attached to carriers 4, which, in turn, are supported by rock arms 1 pivotally mounted on lugs 8 on the inner sides of the shoe members C.

As previously stated, my improved side wall shoe is of such design or construction that when the tank side wall goes out of round, the segmental shoe members C', together with the fabric sealing elements F between the ends of said members, are pulled or pushed circumferentially around the tank side wall without producing a substantial change in the width of the spaces X between the shoe members, and without subjecting the fabric sealing elements to strains tending to disrupt said elements or tear them away from the shoe members. In other words, the shoe members, in addition to being mounted on the iioating roof in such a manner that they are capable of moving circumferentially, are combined with a means which actually causes said shoe members to move circumferentially and also governs or controls the width of the spaces X between the ends of the shoe members, closed by the fabric sealing elements F.

In the form of my invention shown in Figures I to 6, the means just referred to comprises chains or similar flexible devices D, attached to the ends of the shoe members so as to limit relative circumferential movement of adjacent shoe members in a direction to increase the width of they spaces X between said members, thereby governing or determining the maximum circumferential length ofthe annular shoe, and horispaces X, thereby governing or determining the minimum circumferential length of the annular shoe. As shown in Figures l and 2, the stop plates 5 are welded or rigidly attached to the' previously mentioned clamping plates 2 carried by the shoe members C, and each stop plate 5 is provided at its outer end with a rightangu-v larly-disposed stop or abutment piece. When the annularshoe is arranged in the zone or portion of the tank wall of maximum circumferential length, the stops or abutment pieces on the stop plates 5 of adjacent shoe members, are out of contact with each other, as shown clearly in Figure 2. If, for any reason, the friction between the tank side wall and one of the shoe members C causes said shoe member to move circumferentially relatively to the roof E, the stop plate 5 on the forward end of that particular shoe member imparts a forward push to the shoe members in advance of said moved or moving shoe member, and the chain D attached to the rearward end of that particular shoe member exerts a forward pull on the shoe members located behind or at the rear of said moved or moving shoe member. Thus, it will be seen that in my improved side wall shoe, the chains D and stop plates 5 actually move the shoe members C circumferentially; they cause the spaces X between the shoe members to remain constant, or practically so; and they limit the flexing or wrinkling 0f the fabric sealing elements F and prevent said elements from being subjected to destructive stresses. My broad idea contemplates the use of anysuitable means for attaining the results just described. Accordingly, in Figure 8 of the ,drawings I have shown stop plates 5a and 5b attached to the opposed ends of adjacent shoe members C, and constructed so that in addition to limiting relative circumferential movement of the shoe members in a direction to reduce the width of the spaces X, they also limit relative movement of the shoe members in the opposite direction, or in other words, to increase the width of the spaces X. This result is attained by providing each of the stop plates 5b with a hook-shaped portion 5G, arranged so that when two adjacent stop plates move relatively to each other in a direction to increase the width of the space X, the hook shaped portion 5c on the plate 5b contacts with the right-angularly-disposed abutment piece on the plate 5, thus arresting relative movement of said plates and causing one of said plates to exert a pull on the other plate. Relative movement of said stop plates in the opposite direction, i. e., to reduce the width of the space X between the shoe members that carry said stop plates, causes the right-angularly-disposed abutment pieces on said stop plates to come into engagement with each other, as shown in broken lines in Figure 19, thereby arresting relative movement of said plates and resulting in one stop plate imparting a push to the other stop plate.

As previously statedy any suitable mechanism may be used to mount the shoe membersl C on the iioating roof E, so long as said mechanism is of such construction that it permits the shoe members to move inwardly and outwardly relatively to the tank side wall, and also move circumferentially a limited distance relatively to the tank side wall when said wall goes out ofA round. In the drawings I have illustrated the annular sidewallescasas 7 tshoe as being supported by a mechanism f the kind disclosed in my U. S. Patent No, 2,313,856, dated March 16, 1943. Said mechanism comprises a plurality of horizontally-disposed supporting members I arranged in spaced relation 'on the top side of the roof around the peripheral portion of same, as shown in Figure 6, and mounted so that in addition to being capable of moving inwardly and outwardly,rthe outer ends of said supporting members II) are capable Vof, a limited swinging movement clockwise and counter-clockwise. The supporting members IU are capable of moving independently of each other, and` all of Said members are mounted in such a way that during the reciprocating and swinging movement of said members, they vare held against vertical movement, either upwardly or Y downwardly. VTwo supporting members I0 are preferably provided for each segmental Ashoe member C, and the outerends of the supporting members I0 are pivotally connected to lugs 9 on the inner sides'of the shoe members, as shown in Figure 5.

Each supporting member I0 is reciprocatingly.

mounted between a relatively wide, horizontallydisposed roller II on which the bottom edgerof said, member bears, and a roller I4 on which the top edge of said member bears, the roller II being carried by a pair of uprights I3 between which the member I0 is positioned, and the roller I4 being Ycarried by a pair ofuprights I5.Y Stops I2 g and I6 on the uprights I3 and I5, respectively, co-operate with the rollers I I and I4 to maintain the supporting member I0 in a horizontal plane, and absorb the strains and loadsswhich the annular shoeexerts on the supporting members III when -the roof E moves upwardly and downwardly. The roller II is made long enough and the uprights I3 are spaced far enough apart, to permitthe front end of themember l0 to swing laterally a limited-distance, clockwise and counter-clockwise, when said member reciprocates inwardlyandoutwardly relatively to the roof.` A pair of tension springs I1 that are attached at one end to lugs I8 on the roof and attached at their opposite ends to a cross bar I'Ia that is rigidly fastened to the inner end of the supporting member I0, exert an outward thrust on said member and tend to hold said member in a position in which it is disposed in radial relationship with the roof. Whenever the front end of the supporting member swings to the right or to the left, so as-to permit circumferential movement of the annular side wall shoe, sufficient tension isv built up in one of the springs I1 to restore the supporting member to its radial position, immediately upon cessation of the force or pressure that caused the side wall shoe to move circumferentially.

' `As previously stated, my improved side wall shoe or seal is particularly adapted for use with a tank side wall of gradually decreasing internal circumference from its lower towards its upper end, due to the fact that the fabric sealing elements F are so proportioned and combined with the shoe members C, that said fabric elements are straight and fully distended when the anconnected together by rivets, the vbottoni ring A constituting the side wall zone of maximum diameter, and the top ring A4 constituting the zone of minimum diameter. In a conventional oil tank of this construction and having a diameter of ft. the internal circumference of the top ring'A is only about 11 inches shorter than the internal circumference of the bottom ring A. Hence, the total contraction of all of the fabric sealing elements F is only about 11 inches, which amount is negilgible, if said 1lV inches is equally absorbed by a large number of flexible members F. If 40 members F are used, then each absorbs only about one-fourth of an inch.

Prior to my present invention, it was impossible to make the secondary seal in the form of a continuous ring around the inside of the tank wall with a multi-shoe design, without creating relatively large loops in the fabric of which the secondary seal was constructed, due to the fact that the fabric sealing elements between the ends of the segmental shoe members had to be installed with several inches of slack. This necessitated cutting and lapping the secondary seal fabric for each shoe member length with attendant great expense and inefficiency in obtaining a wind-proof secondary seal. The shoe members were usually 21/'2 to 3 ft. long, and were supported from the roof by devices that compelled the shoe members to move to and from the tank side wall substantially in a radial plane. Actual experiments on tanks equipped with a floating roof show that when a tank wall is l0 inches more out of round at one'height than another, some of the vertical elements of said wall move circumferentially 3 inches or 4 inches relative to the floating roof, which remains round. If the centers of the shoe members must remain on the same radius of the roof as they move in and out, it canreadily be seen that the fabric sealing elements of some of the shoe members (and hence all of the shoe members, because it is unknown which ones will require it) must be able to separate 3 or 4 inches as the roof moves up and down. This condition necessitated excessive adjustability of the fabric sealing elements between the shoe members, and hence, prevented the secondary fabric seal from being attached to the annular side wall seal in a continuous piece, without making such large wrinkles in the secondary fabric that large spaces were produced between the contacting portions of the secondary fabric and the tank side wall. In addition to the above necessity for adjustability of the fabric sealing elements between the shoe members, is that required by the change in internal circumference of the tank.

We have then, as the art now stands, three reasons for requiring several inches of adjustability of the fabric sealing elements between the shoe members:

1. The change in roundness of the tank at different elevations of the floating roof;

2. The change in internal circumferentiav length of the tank side wall; and

3. An additional amount caused by the old method of installing the supporting devices for the segments or sections of the shoe.

I propose to eliminate 1 and 3 above, leaving only 2, i. e., the adjustability required byv the change of internal circumference, to be accommodated by the fabric elements between the shoe members. Ido this by v Y l. Making the entire length of the annular side wall seal (shoe members plus spaces X) no longer than the largest circumference ofthe tankside wall, under which conditions the fabric sealing the maximum amount of spaces X during the operation of the roof;

(c) Installing the second shoe member and each succeeding shoe member with chains D tight, wedging the adjacent shoe members apart and wedging each shoe member as it is installed against the tank wall;

(d) Measuring the last shoe member, designated by the reference character C in Figure 6 and cutting it off on the job to make space X correct;

3. Supporting the shoe members C on devices which allow the seal or annular shoe as an entirety to move several inches circumferentially as Well as radially relative to the floating roof.

After all the shoe members are in place, the fabric sealing elements are installed either by cementing or clamping them to the vertical edges of adjacent shoe members. Said fabric elements F may be substantially tight at the elevation of the chains D. I prefer, however, to make said fabric elements l inch wide, more or less, at the bottom than at the top, and thus allow considerably more adjustment between the shoe members at the bottom than at the top. Wrinkles in the elements F below their ponits of attachment to the primary fabric H do not affect the primary seal H nor the secondary seal G, and hence, do not affect the wrinkling of H and G. This is to take care of the condition where one end of a shoe member may be higher than the other which causes more gap at the bottom than where the chain D is located. Thus, no strain can ever be applied to the fabric sealing elements to tear them, even after they are very old.

The general method of installing the shoes has previously been briefly described. In more detail, the following is the preferred procedure:

1. Install the rst shoe members on two supporting members i0, so that each of said members IIJ is in the center of its supporting roller l l. Press the shoe member snugly against tank side wall and hold it there. Also wedge it with a block between the shoe member and roof, so that it cannot move circumferentially v 2. With a template mark off the location of the supporting members i i) for the second shoe member and install said members I 3. Set second shoe member on its supporting members IU, install chain D, and wedge shoe members apart until chain is tight;

4. Proceed around tank until the last full length shoe member is in place. Then measure the odd remaining gap and cut the last shoe member C' to fit so that the final space X is such that the last chain is tight;

5. Install the fabric sealing elements F;

6. Install the primary fabric I-I on the floating roof and atach it to the shoe members C and to the fabric elements F, usually by cementing or sewing the primary fabric to the elements F;

7. Install the secondary fabric G and preferably cement or sew same to the fabric elements F, although this is not necessary, so long as the secondary seal laps over and extends downwardly over the sealing elements F; and

8. Remove all wedges and the sealing structure is ready to operate.

As the tank fills, the annular shoe progressively passes to smaller and smaller rings of the tank side wall, whereupon the fabric sealing elements F flex, at rst very slightly, the maximum lexure being in the top ring. If the tank is out of round (and practically all oil tanks are), some of the shoe members will move circumferentially with regard to the roof, but this causes no flexure of the fabric sealing elements F. As the tank empties, the process will reverse itself The fabric sealing elements F will straighten and the shoe members that moved circumferentially relative to the roof will move back to their original `positions. When the roof is back to the position where the sealing structure was erected, all the fabric sealing elements F will have straightened to their original position and the shoe members will have their same relationship circumferentially with reference to the roof.

In order to more clearly describe my invention and explain the operation of my improved side wall shoe or seal, I have incorporated two views, Figures 10 and 11, which are intended to illustrate diagrammatically the old way of constructing a side wall shoe made up of segmental shoe members and fabric sealing elements extending across the gaps between said members and my new way of constructing such a side wall shoe. In Figure 10 the tank side wall is shown in solid lines in its round or circular condition, and is shown in broken lines in its out-of-round or oval condition. That half of Figure 10 designaed by `the legend Half circle I-Old way is intended to illustrate the principle of operation of an annular side wall shoe provided with twelve segmental shoe members whose centers move in and out on radii of the roof, and the remainder of said figure is intended to illustrate the principle of operation of my improved side wall shoe comprising twelve shoe members whose centers move in and out and sidewise around the tank side wall, not on a roof radius. In Figure 10, L, M, N, O, P, Q, R and S are points on the ltank side wall when said wall is round, and L', M', N', O', P', Q', R', and S' are the same points on the tank side wall when said wall is out of round.

By actual test, the distances PP', QQ', RR', and SS' are 4 inches under the conditions shown in the drawing, 'which is for a tank 30 ft. in diam. and 10 inches out of round. Therefore, SL'P is 8 inches shorter than SLP and QM'R is 8 inches shorter than OMR. And PN 'R is 8 inches longer than PNR and SO'Q is 8 inches longer than SOQ.

Consider half circle I--old way, where center of shoe members move in and out on a radius of the roof. It can be seen from Figures l0 and 11 that the ends of shoes c and a nearest to P and S, respectively, move sidewise practically none. This means that the two fabric sealing elements between shoes d, c and da must take up practically all the 8 inch shortening along the PL'S. There are only two gaps K to do this in this quadrant. Therefore, each gap K must shorten a little less than 4 inches each. In other words, if shoe members more in and out on a roof radius, there are less than one fourth of the gaps available to take care of the shortening, due to out of roundness. Therefore, K is about 4 inches shorter than K. Similarly, K is about 4 inches longer than K. Since it is necessary to have any gap either lengthen or shorten, it is seen thatI for the conditions described, every gap must have a total 11 adjustability of 8 inches. This 8 inches may be compared to one half inch adjustment per gap required to allow for 6 inch change in circumference, when each of the twelve gaps takes up its equal quota of the 6 inch, and does not have to c take up anything for the side shift described.

Consider half circle II-K is constant, .because shoe members move sidewise as much as is necessary to keep K constant. Thus, it is seen that there is no adjustment required in the fabric sealing elements for this purpose, which turns out to be the major reason for having the fabric sealing elements between the segmental shoe members. Thus, it will be seen, that my improved annular shoe comprises segmental shoe members with circumferential adjustments between their ends, which shoe members can move sidewise, plus means for causing said shoe members, as an entirety, to operate like a single annular shoe, i. e., a continuous side wall shoe which forces its segments to move as an entirety in a circumferential direction to allow for the change in roundness of the tank shell. Of a necessity, to attain this result, it can be seen that the entire adjustability of all the gaps between the shoe members must be substantially only that amount which is required by the change in circumference of the tank side wall.

The above is the main object oi' my invention.

Another object is to equip a segmental shoe member side wall seal with a secondary seal which is a continuous member between the shoe members and around the tank side wall. Said second object is attainable as a result of the first, i. e., because each gap takes an equal quota of the total changes required, which is very small, and because that total change is only the change in circumference and does not include the side shift required by change in roundness.

Another way of stating the rst object is, a Y

segmental shoe member side wall seal, limited as to its maximum length as'an entirety to a maximum length which is preferably substantially the greatest internal length of the tank side wall, and limited as to its minimum length to substantially the smallest internal length of the tank side Wall.

Another way of stating the first object is, a side wall seal comprising segmental shoe members so controlled that the gap between adjacent shoe members takes substantially an equal proporo tion of any required adjustment of the seal.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The combination of a liquid storage tank provided with a circular side wall which at times is liable to flex and go out of round, a circular roof adapted to'be supported by the liquid in the tank, a sealing means for the space between the roof and the tank side wall comprising a exible shoe composed of an annular row of segmetal shoe members, disposed vertically in sliding engagement with the tank side wall and with their ends at all times, separated by gaps, gas

tight, fabric sealing elements attached to the end portions of said shoe members and bridging the gaps between said members, said sealing elements -being of such width that said elements are substantially free of wrinkles when the gaps between said shoe members are of maximum Width, a supporting mechanism for mounting said shoe members on the roof, having provision for permitting each shoe member to move radially and also move circumferentially a limited distance to the right and to the left,v and co-operating push and pull devices on said shoe members constructed so as to co-act with each other to limit sidewise movement of said members towards and away from each other for the purpose of controlling both the maximum and minimum width of the gaps between said shoe members and also to transmit movement from one shoe member to the other in a circumferential direction in the event the tank side wall flexes out of round and creates a force which is exerted in a circumferential direction on one or more groups of said shoe members, thereby causing all of the shoe members of said annular row to move as a unit, circumferentially of the roof, without substantially altering the Width of the gapsbetween said shoe members.

2. A structure of the kind described in claim 1, in which the tank side wall gradually decreases in internal circumference from its lower end towards its upper end and in which the fabric sealing elements have fullness of such a degree that the combined fullness of all of the fabric sealing elements corresponds approximately to the difference in internal circumference between the lower and upper ends of the tank side wall, thereby causing said sealing elements to be maintained in a substantially taut condition when the annular row of shoe members is located in the zone of the tank side wall that is of maximum internal circumference, and to be maintained in only a slightly puckered or wrinkled condition when said row of shoe members is located in the Zone of said tank side wall that is of minimum internal circumference.

" JOHN H. WIGGINS.

REFERENCES CITED The following references are of record in the lile of this patent:

UNITED STATES PATENTS Netherlands Sept. 16, 1930 

